Transcript DIESEL ENGINES - Pomorski fakultet, Sveučilište u Rijeci

Lesson 5
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Rudolf Diesel-1892-high-compression, selfignition engine (intended to burn powered
coal)
Herbert Akroyd Stuart-1888-oil fuel was
ignited by compressing the mixture of oil+air
in contact with a hot wall in the combustion
chamber
the pressure was permanently increased → hot
surfaces were not needed any more for the
ignition
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main or auxiliary propelling machinery
OPERATING CYCLE:
two-stroke cycle
four-stroke cycle
CYCLE – a series of steps following each other
STROKE – a single up or down movement
 single acting engines
 double- acting engines
 opposed piston engines
Single acting engine – one end of the cylinder to develop power
Double-acting engine – both ends of the cylinder / both piston faces
- complicated construction
- low speed units
- pistons shorter than in single acting engine
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In-line cylinder arrangement
“V” arrangement of cylinders
Flat arrangement of cylinders
Radial arrangement of cylinders
Low speed: > 200 rev/min
Medium speed: 200 – 600 rev/min
High speed: < 600 rev/min
Trunk piston engine (piston directly connected to
the rod)
Crosshead – type engine (piston indirectly
connected to the rod = piston rod /
crosshead)
Direct drive = direct coupled engines (coupled
directly to the propeller shafting)
Geared engines = indirect drive (coupled to a
reduction gearing)
Direct – reversible engine
(clockwise & anticlockwise rotation)
Non-reversible engine
(unidirectional engines)
1. INDUCTION: crankshaft rotates clockwise and
the piston moves down the cylinder, inlet valve
is open and a fresh charge of air is drawn into
the cylinder.
2. COMPRESSION: inlet valve has closed and the
charge of air is compressed by the piston as it
moves up the cylinder. Because energy is being
transferred into the air, its pressure and
temperature increase. By the time the piston is
approaching the TDC the pressure is over 100
bar and the temperature over 500°.
3. POWER: Just before TDC fuel is injected into
the cylinder by the fuel injector. The fuel is
"atomised" into tiny droplets. Because they are
very small these droplets heat up very quickly
and start to burn as the piston passes over
TDC.
4. EXHAUST: As the piston approaches the BDC,
the exhaust valve starts to open. As the piston
now moves up the cylinder, the hot gases are
expelled from the cylinder. As the Piston
approaches TDC again the inlet valve starts to
open and the cycle is repeated.
1. The crankshaft revolves clockwise and the
piston moves up the cylinder, compressing the
charge of air. Because energy is being
transferred into the air, its pressure and
temperature increase. By the time the piston is
approaching the TDC the pressure is
over 100 bar and the temperature
over 500°C.
2. Just before TDC fuel is injected into the cylinder
by the fuel injector. The fuel is "atomised" into
tiny droplets. Because they are very small these
droplets heat up very quickly and start to burn
as the piston passes over TDC.
The expanding gas from the fuel burning in the
oxygen forces the piston down the cylinder,
turning the crankshaft. It is during this stroke
that work energy is being put into the engine;
during the upward stroke of the piston.
3. As the piston moves down the cylinder, the
useful energy from the burning fuel is expended.
At about 110° after TDC the exhaust valve opens
and the hot exhaust gases begin to leave the
cylinder.
4. At about 140º after TDC the piston uncovers a
set of ports known as scavenge ports. Pressurised
air enters the cylinder via these ports and pushes
the remaining exhaust gas from the cylinder in a
process known as "scavenging".
The piston now goes past Bottom Dead Centre
and starts moving up the cylinder, closing off the
scavenge ports. The exhaust valve then closes and
compression begins.
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http://www.youtube.com/watch?v=x9yS2xdP
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http://www.youtube.com/watch?v=MW1jixD
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